Github user jinfengni commented on the issue:
https://github.com/apache/drill/pull/819
Regarding Paul's suggestion of using sampling (either 1st batch, or `n`
batches), if the sampled length is returned to client as metadata for query
result set, it could cause quite big problems for client. If the sampled max
length is 5, client expects to see varchar up to 5 chars. If a new batch
arrives with varchar(10), it would either crash the client, or make the client
show incorrect result. AFAIK, that's exactly what happened when Sean was
working on 'LIMIT 0' optimization, and if there is an inconsistency of the type
returned between 'LIMIT 0' and one returned from a regular query.
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